Optical coupling device, manufacturing method thereof, and power conversion system

ABSTRACT

In order to improve properties, an optical coupling device has a potting resin and an internal mold resin between a light emitting element and a light receiving element. The internal mold resin is a cured product of a composition having an epoxy resin and a curing agent, and is a resin having a light transmission property. Additionally, the internal mold resin MRI contains an aromatic ring and an alicyclic compound. By thus lowering the ratio of an aromatic ring in the epoxy resin, deterioration of the resin can be suppressed. Thereby, a decrease in the light transmission property of the epoxy resin cured product can be suppressed, and degradation of the transmission performance for an optical signal can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/941,719, filed Nov. 16, 2015 which is the disclosure of JapanesePatent Application No. 2015-035604 filed on Feb. 25, 2015 including thespecification, drawings and abstract is incorporated herein by referencein its entirety.

BACKGROUND

The present invention relates to an optical coupling device, amanufacturing method thereof, and a power conversion system.

A photocoupler has a light emitting element, such as a light emittingdiode, and a light receiving element, such as a phototransistor, andtransmits an electrical signal by converting an inputted electricalsignal into light with the light emitting element and by returning thelight to the electrical signal with the light receiving element.

A photocoupler is disclosed, for example, in Japanese Unexamined PatentApplication Publication No. 2008-189833 (Patent Document 1), in which alight emitting element and a light receiving element are sealed by acured product of a thermosetting epoxy resin composition.

Also, a photocoupler using a primary sealing resin and a secondarysealing resin is disclosed in Japanese Unexamined Patent ApplicationPublication No. 2014-33124 (Patent Document 2). The primary sealingresin contains an epoxy resin for primary sealing, a phenolic resincuring agent for primary sealing, an inorganic filler for primarysealing, and fatty acid wax for primary sealing; and the secondarysealing resin contains an epoxy resin for secondary sealing, a phenolicresin curing agent for secondary sealing, an inorganic filler forsecondary sealing, and fatty acid wax for secondary sealing. At leastone of the resin for primary sealing and the resin for secondary sealingcontains fatty acid amide wax.

Also, an optical semiconductor device sealed by a cured product of anepoxy resin composition is disclosed in Japanese Unexamined PatentApplication Publication No. 2005-239901 (Patent Document 3). The epoxyresin composition is one whose main components are an epoxy resin (A)having two or more epoxy groups in one molecule, a phenolic resin curingagent (B), a curing accelerator (C), and fused crushed silica (D). Theepoxy resin composition further contains a phenolic antioxidant (E) asan essential component. Additionally, the light transmittance of a curedproduct of the epoxy resin composition, the product having a thicknessof 1 mm, is 15% or more for the light having a wavelength of from 700 nmto 1000 nm, and the light transmittance retention rate thereof afterbeing subjected to 125° C. for 1000 hrs is 50% or more for the lighthaving a wavelength of 720 nm.

PRIOR ART DOCUMENT

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2008-189833

[Patent Document 2] Japanese Unexamined Patent Application PublicationNo. 2014-33124

[Patent Document 3] Japanese Unexamined Patent Application PublicationNo. 2005-239901

SUMMARY

As described above, a photocoupler has a light emitting element, such asa light emitting diode, and a light receiving element, such as aphototransistor, and transmits an electrical signal by converting aninputted electrical signal into light with the light emitting elementand by returning the light into the electrical signal with the lightreceiving element.

According to such a signal transmission technology using light, signaltransmission paths can be electrically separated from each other. Thatis, a signal can be transmitted, via light, between a primary electricalcircuit and a secondary electrical circuit that are electricallyinsulated from each other.

It is necessary that a light emitting element on the side of the primaryelectrical circuit and that on the side of the secondary electricalcircuit are insulated from each other by a resin having a lighttransmission property.

However, according to the study by the present inventors, it has beenconfirmed in a photocoupler that the light transmission property of aresin is decreased due to discoloration of the resin, and hence there isa need for the improvement thereof.

Other problems and new characteristics will become clear from thedescription and accompanying drawings of the present specification.

Of the preferred embodiments disclosed in the present application,outlines of the typical ones will be briefly described as follows.

An optical coupling device described in one embodiment disclosed in thepresent application has a first resin and a second resin between a firstelement and a second element. The second resin is a cured product of acomposition having an epoxy resin and a curing agent, and has a lighttransmission property. Additionally, the second resin contains anaromatic ring and an alicyclic compound.

A manufacturing method of an optical coupling device described in oneembodiment disclosed in the present application includes the steps of:forming a first resin over a first element; and forming a second resinbetween a second element and the first resin after facing the firstresin over the first element and the second element each other. Thesecond resin is a cured product of a composition having an epoxy resinand a curing agent, and has a light transmission property. Additionally,the epoxy resin contains an aromatic ring and an alicyclic compound.

A power conversion system described in one embodiment disclosed in thepresent application is one including an amplifier circuit part, and anoptical coupling part to be coupled to the amplifier circuit part. Theoptical coupling part has a first resin and a second resin between afirst element and a second element. The second resin is a cured productof a composition having an epoxy resin and a curing agent, and has alight transmission property. Additionally, the second resin contains anaromatic ring and an alicyclic compound.

Advantage of the Invention

According to an optical coupling device described in the typicalembodiments that are disclosed in the present application and describedbelow, discoloration of a resin in the device can be suppressed and theproperties of the device can be improved.

According to a manufacturing method of an optical coupling device,described in the typical embodiments that are disclosed in the presentapplication and described below, an optical coupling device, in whichdiscoloration of a resin in the device is suppressed and good propertiesare achieved, can be manufactured.

According to a power conversion system described in the typicalembodiments that are disclosed in the present application and describedbelow, discoloration of a resin in a device that forms the powerconversion system can be suppressed and the properties of the system canbe improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating a configuration of an opticalcoupling device according to First Embodiment;

FIG. 2 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment;

FIG. 3 is a plan view illustrating a manufacturing step of the opticalcoupling device according to First Embodiment;

FIG. 4 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 2;

FIG. 5 is a plan view illustrating a manufacturing step of the opticalcoupling device according to First Embodiment, the step following thatof FIG. 3;

FIG. 6 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 4;

FIG. 7 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 6;

FIG. 8 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 7;

FIG. 9 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 8;

FIG. 10 is a sectional view illustrating a manufacturing step of theoptical coupling device according to First Embodiment, the stepfollowing that of FIG. 9;

FIG. 11 is a sectional view illustrating a configuration of an opticalcoupling device of First Comparative Example;

FIGS. 12(A) to 12(C) are schematic views illustrating a mechanism bywhich a void is produced in a resin interface;

FIGS. 13(A) to 13(C) are schematic views illustrating a mechanism bywhich a resin is discolored;

FIG. 14 is a view schematically illustrating a reaction in which anaromatic ring undergoes oxidation discoloration;

FIG. 15 is a sectional view illustrating a configuration of an opticalcoupling device of Second Comparative Example;

FIGS. 16(A) to 16(C) are schematic views illustrating a mechanism bywhich discoloration of a resin is suppressed;

FIGS. 17(A) to 17(C) are schematic views illustrating states of voids,when a silicone resin cured product having a low hardness is used;

FIGS. 18(A) to 18(C) are schematic views illustrating states of a void,when a silicone resin cured product according to Second Embodiment isused; and

FIG. 19 is an illustrative view illustrating one example of a powerconversion system according to Third Embodiment.

DETAILED DESCRIPTION

If needed for convenience, the following embodiments will be describedby dividing each of them into multiple sections or embodiments; however,the multiple sections or embodiments are not irrelevant to each other,but they are in a relationship in which one is a variation, applicationexample, detailed description, or supplementary description of part orthe whole of the others, unless otherwise indicated. When the numbers ofelements, etc. (including numbers of pieces, numerical values, amounts,ranges, etc.) are referred to in the following embodiments, the numbersare not limited to the specific ones but may be more or less than thespecific numbers, unless otherwise indicated or except when the numbersare obviously limited to the specific numbers in principle.

Further, in the following embodiments, the constituents (also includingelement steps, etc.) are not necessarily essential, unless otherwiseindicated or clearly essential in principle. Similarly, when the shapesand positional relations, etc., of the constituents, etc., are referredto in the following embodiments, those substantially the same or similarto the shapes, etc., should also be included, unless otherwise indicatedor except when considered to be clearly otherwise in principle. The sameis true with the aforementioned numbers, etc., (including the numbers ofpieces, numerical values, amounts, and ranges, etc.).

Hereinafter, preferred embodiments will be described in detail withreference to the accompanying views. In the whole views for explainingthe embodiments, members having the same function as each other will bedenoted with the same or relevant reference numeral and duplicativedescription will be omitted. When a plurality of similar members (parts)are present, an individual or specific part may be represented by addinga sign to the collective reference numeral. In the followingembodiments, description of the same or similar parts will not berepeated in principle, unless particularly necessary.

In the views used in the embodiments, hatching may be omitted even insectional views in order to make them easier to see. Alternatively,hatching may be added even in plan views in order to make them easier tosee.

In a sectional view or a plan view, the size of each part does notcorrespond to that of an actual device, and a specific part may bedisplayed to be relatively large in order to make the view easier tounderstand. The same is true with the case where a sectional view and aplan view correspond to each other.

First Embodiment

Hereinafter, an optical coupling device according to the presentembodiment will be described in detail with reference to theaccompanying drawings.

[Structure Description]

FIG. 1 is a sectional view illustrating a configuration of an opticalcoupling device according to the present embodiment. The opticalcoupling device according to the embodiment is a photocoupler. Theoptical coupling device according to the embodiment illustrated in FIG.1 has a light emitting element LED, a light receiving element PD, andtwo types of resins (PR, MRI) arranged between them. An electricalsignal can be transmitted by converting an inputted electrical signalinto light with the light emitting element LED and by returning thelight to the electrical signal with the light receiving element PD.

The light emitting element (light emitting chip) LED is a photoelectricconversion element that receives an electrical signal to output anoptical signal. A light emitting diode using, for example, GaAs, AlGaAs,or the like, can be used as the light emitting element LED. The lightemitting element LED is mounted over a chip mounting part DP1. The chipmounting part DP1 is a plate-shaped member including a metal, such as,for example, copper (Cu). The light emitting element LED is fixated(adhered, fixed) over the chip mounting part (die pad) DP1 via a diebond material. The die bond material (mounting material) is a conductiveadhesive (conductive paste). Two leads LD1 are arranged around the chipmounting part DP1. One of the two leads LD1 is coupled to the chipmounting part DP1 (see FIG. 3). The surface electrode of the lightemitting element LED and the other lead LD1 are electrically coupledtogether via a wire W1. The wire W1 is a linear member (thin metal wire)including a metal material, such as, for example, gold (Au).

A potting resin PR is formed over the light emitting element LED. Inother words, the light emitting element LED over the chip mounting partDP1 is covered with the potting resin PR. It is necessary that thepotting resin PR has an insulation property and has a light transmissionproperty for the light having the wavelength of an optical signal. Forexample, a silicone resin cured product, or the like, can be used as thepotting resin PR. In the present embodiment, a mixture of variouscompounds to be used as materials for resins (PR and later-describedMRI) is referred to as a “resin composition”, and a cured product ofthis composition is referred to as a “resin cured product”.

A silicone resin cured product is a high molecular compound having, asamain chain, an organopolysiloxane (structure having both an —Si—O—Si—O—chain as a main chain and an organic group over Si).

The silicone resin cured product has a light transmission property forthe light having the wavelength of an optical signal. For example, thetransmittance per mm of the thickness of the silicone resin curedproduct is 10% or more for the light having a wavelength within a rangeof 700 nm to 1000 nm. Further, the reflectance per mm of the thicknessof the silicone resin cured product is 90% or less for the light havinga wavelength within a range of 700 nm to 1000 nm.

In order to improve the strength of the silicone resin cured product, afiller, such as silica, may be mixed into a silicone resin composition.The content of a filler (e.g., silica) is preferably 20 wt % or less,and more preferably 0 wt %. When being coated, i.e., before being cured,the silicone resin composition has a liquid state. If the content of afiller is more than 20 wt %, the flowability of the silicone resin isdecreased. Accordingly, the circumference of the light emitting elementLED cannot be uniformly filled with the resin, causing the covering ofthe light emitting element LED to be decreased. If the content of afiller is more than 20 wt %, the hardness of the silicone resin, afterbeing cured, becomes too large, and it becomes difficult to fullyrelieve the stress applied to the light emitting element LED.

The light receiving element PD is a photoelectric conversion elementthat receives an optical signal to output an electrical signal. Forexample, a photodiode, a phototransistor, a light receiving IC, or thelike, can be used as the light receiving element PD. The light receivingelement PD is mounted over a chip mounting part (die pad) DP2. The chipmounting part DP2 is a plate-shaped member including a metal, such as,for example, copper (Cu). The light receiving element PD is fixated(adhered, fixed) over the chip mounting part DP2 via a die bondmaterial. The die bond material (mounting material) is a conductiveadhesive (conductive paste). A plurality of leads LD2 are arrangedaround the chip mounting part DP2. One of the leads LD2 is coupled tothe chip mounting part DP2. The surface electrodes of the lightreceiving element PD and the other leads LD2 are electrically coupledtogether via a wire W2, respectively. The wire W2 is a linear member(thin metal wire) including a metal material, such as, for example, gold(Au).

The light receiving element PD and the light emitting element LED arearranged to face each other. That is, the chip mounting parts DP1 andDP2 are arranged up and down so as to be spaced apart from each other bya certain distance, and the light emitting element LED is arranged belowthe chip mounting part DP1, and the light receiving element PD above thechip mounting part DP2, as illustrated in FIG. 1. Herein, the lightemitting element LED is covered with the potting resin PR. The pottingresin PR is a translucent resin.

The space between the potting resin PR and the light receiving elementPD and the outer periphery of them are sealed by an internal mold resin(translucent mold resin) MRI. The outer periphery of the internal moldresin MRI is sealed by an external mold resin (light-shielding moldresin) MRO.

An epoxy resin cured product (cured product of an epoxy resincomposition) can be used as the internal mold resin MRI. The epoxy resincured product does not contain a reflecting agent, such as titaniumoxide, and has a light transmission property for the light having thewavelength of an optical signal. For example, the transmittance per mmof the thickness of the silicone resin cured product is 10% or more forthe light having a wavelength within a range of 700 nm to 1000 nm.Further, the reflectance per mm of the thickness of the silicone resincured product is 90% or less for the light having a wavelength within arange of 700 nm to 1000 nm.

The epoxy resin cured product is formed by a reaction between the mainagent and the curing agent in the epoxy resin composition. The epoxyresin composition can be cured and highly polymerized by crosslinkingthe epoxy groups in the main agent (epoxy resin) via the curing agent.Each of the main agent and the curing agent may be any of a monomer,from a dimer to a pentamer, an oligomer (below icosamer) and aprepolymer.

A compound, in which the ratio of an aromatic ring is small, is used asthe main agent. For example, cycloaliphatic epoxy resins (e.g.,dicyclopentadiene-based epoxy resin, etc.), epoxy resins having anitrogen-containing ring (e.g., triazine ring-based epoxy resin, etc.),and the like, can be used as the main agent in which the ratio of anaromatic ring is small. A compound represented by the following formula(1) can be used as the dicyclopentadiene-based epoxy resin.Alternatively, a compound excluding an aromatic ring may be used as themain agent.

A compound, in which the ratio of an aromatic ring is small, is used asthe curing agent. More preferably, a compound excluding an aromatic ringis used. For example, an acid anhydride curing agent, etc., can be usedas the curing agent excluding an aromatic ring. A compound representedby the following formula (2) can be used as the acid anhydride curingagent.

By thus using a compound, in which the ratio of an aromatic ring issmall, as the main agent, the ratio of an aromatic ring in the epoxyresin cured product becomes small, thereby allowing deterioration of theresin to be suppressed.

Further, by using a compound, in which the ratio of an aromatic ring issmall, as the curing agent, the ratio of an aromatic ring in the epoxyresin cured product becomes small, thereby allowing deterioration of theresin to be suppressed.

Hereinafter, a reaction between a main agent, in which the ratio of anaromatic ring is large, and a curing agent, in which the ratio of anaromatic ring is large, will be described. With a reaction of acomposition having: a compound represented by the following formula (3)as the main agent; and a compound represented by the following formula(4) as the curing agent, a compound represented by the following formula(5), which is an epoxy resin cured product, can be produced. That is, anepoxy group in the compound represented by the formula (3) reacts withan OH group in the compound represented by the formula (4), so that apolymerization reaction progresses (see the portions enclosed by thedashed lines in the formulae (3), (4), and (5)).

If such a main agent, in which the ratio of an aromatic ring is large,and such a curing agent, in which the ratio of an aromatic ring islarge, are used, the ratio of an aromatic ring in an epoxy resin curedproduct becomes large.

On the other hand, by using a main agent, in which the ratio of anaromatic ring is small, and a curing agent, in which the ratio of anaromatic ring is small, the ratio of an aromatic ring in an epoxy resincured product can be made small, thereby allowing deterioration of theresin to be suppressed. Details will be described later.

In an epoxy resin cured product to be used as the internal mold resinMRI, a filler, such as silica, may be mixed into an epoxy resincomposition in order to improve the strength of the product. Further, bymixing a filler, such as silica, the difference between the coefficientof thermal expansion of the lead LD1 or LD2 including a metal and thatof the internal mold resin MRI can be reduced. A filler, such as silica,is mixed, for example, in a ratio of approximately 60 to 90 wt % basedon the weight of the epoxy resin composition (main agent, curing agent).

Additionally, it is preferable not to add a reflecting agent, such astitanium oxide, and a colorant, such as carbon, to an epoxy resincomposition to be used as the internal mold resin MRI, in order tosecure a light transmission property.

An external mold resin MRO is provided to cover the internal mold resinMRI, so that entry of light from the outside is prevented. Accordingly,the external mold resin MRO has a light-shielding property. For example,a black epoxy resin cured product, etc., can be used as the externalmold resin MRO.

In the optical coupling device according to the present embodiment, anelectrical signal is supplied to the light emitting element LED via thelead LD1, and the light emitting element LED emits light in response tothe electrical signal. The light emitted by the light emitting elementLED enters the light receiving element PD via the potting resin(silicone resin cured product) PR and the internal mold resin (epoxyresin cured product) MRI. Then, the light is converted into theelectrical signal in the light receiving element PD, which istransmitted, via the lead LD2, to a device (not illustrated) to whichthe lead LD2 is coupled.

[Description of Manufacturing Method]

FIGS. 2 to 10 are sectional views or plan views each illustrating amanufacturing step of the optical coupling device according to thepresent embodiment.

As illustrated in FIG. 2, the light emitting element LED is mounted overthe chip mounting part DP1 of a lead frame LF. For example, a die bondmaterial (not illustrated) is coated over the chip mounting part DP1 ofthe lead frame LF, and the light emitting element LED is mountedthereover and fixed. The lead frame LF has a structure in which aplurality of combinations of the chip mounting part DP1 and the leadsLD1 arranged at the outer periphery of the part DP1 are interlinked by aframe F. The light emitting element LED is mounted over the chipmounting part DP1 of the lead frame LF. The shape of the lead frame LFis not limited, but for example, the lead frame LF as illustrated inFIG. 3 can be used. As illustrated in FIG. 3, two leads LD1 are arrangedaround the chip mounting part DP1, and one of them is coupled to thechip mounting part DP1.

Subsequently, the surface electrode of the light emitting element LEDand the lead LD1 are coupled together by the wire W1 (wire bondingstep), as illustrated in FIGS. 4 and 5. In FIG. 5, the surface electrodeof light emitting element LED is indicated by a round shape.

Subsequently, the potting resin PR having a liquid or paste form isdropped (coated) over the light emitting element LED over the chipmounting part DP1, so that the light emitting element LED is coveredwith the potting resin PR, as illustrated in FIG. 6. For example, asilicone resin cured product, or the like, is used as the potting resinPR. For example, a liquid silicone resin composition is coated and thencured by being subjected to a heat treatment. Heating temperature is,for example, approximately 160° C. to 200° C. Thereafter, the siliconeresin cured product is cooled to room temperature (normal temperature).

The light emitting element LED can be protected by thus covering it withthe potting resin (silicone resin cured product) PR. In particular, aso-called compound semiconductor, such as GaAs, AlGaAs, or the like, ismostly used for the light emitting element LED. Such a compoundsemiconductor is harder and more brittle as compared to a semiconductor,such as, for example, silicon. Accordingly, the stress applied to thelight emitting element LED using such a material can be relieved bycovering the light emitting element LED with a soft silicone resin curedproduct. A silicone resin cured product has a flexibility higher thanthat of an epoxy resin cured product. In particular, the light-emittingproperty of the light emitting element LED may be degraded due toapplication of stress, but degradation of the light-emitting propertycan be suppressed by covering the element LED with a soft silicone resincured product. Further, the distortion, occurring due to the thermalexpansion difference with the internal resin, can be suppressed bycovering only the vicinity of the light emitting element LED.

Subsequently, the light receiving element PD is mounted over the chipmounting part DP2. For example, a die bond material (not illustrated) iscoated over the chip mounting part DP2 of the lead frame LF, and thelight receiving element PD is mounted thereover and fixed, asillustrated in FIG. 7. The lead frame LF for the light receiving elementPD has a structure in which a plurality of combinations of the chipmounting part DP2 and the leads LD2 arranged at the outer periphery ofthe part DP2 are interlinked by a frame F. Subsequently, a plurality ofthe surface electrodes of the light receiving element PD and the leadsLD2 are coupled together by the wire W2, respectively (wire bondingstep).

Herein, after the light emitting element LED is mounted over the chipmounting part DP1, the light receiving element PD is mounted over thechip mounting part DP2, but the order of these steps is not limited.Additionally, the potting resin PR is not formed over the lightreceiving element PD in FIG. 7, but the potting resin PR may be formedthereover. However, when a semiconductor, such as, for example, silicon,is used as the light receiving element PD, it is not likely to undergostress deformation. Accordingly, the potting resin (silicone resin curedproduct) PR can be omitted.

Subsequently, the lead frame LF over which the light emitting elementLED is mounted and the lead frame LF over which the light receivingelement PD is mounted are faced with each other, so that both the leadframes LF are sandwiched by a forming mold M1, as illustrated in FIG. 8.Herein, the leads LD1 and LD2 of the two lead frames LF may be processedinto a desired shape by press working, etc., if necessary.

An epoxy resin composition is injected (put) into the space (cavity)between the forming mold M1 in the state where the two lead frames LFare being sandwiched by the forming mold M1, and the resin compositionis subjected to a heat treatment so as to form the internal mold resinMRI. A sealing method, in which a sealing resin is supplied to a spaceformed in the forming mold M1 and then cured as stated above, isreferred to as a transfer mold method.

Herein, an epoxy resin cured product is used as the internal mold resinMRI in the present embodiment. In particular, an epoxy resin curedproduct is used, the cured product being formed by the reaction (thermalcuring, polymerization, crosslinking, high polymerization) between theaforementioned main agent and curing agent in each of which the ratio ofan aromatic ring is small. Also in the present embodiment,polymerization progresses with an epoxy group in the main agent reactingwith the curing agent. This reaction progresses by heating. By thusmaking the ratio of an aromatic ring in the epoxy resin cured productsmall, deterioration of the resin can be suppressed as described later.Thereby, degradation of the light transmission property of the epoxyresin cured product can be suppressed, and degradation of thetransmission performance for an optical signal can be reduced. Heatingtemperature is, for example, approximately 160° C. to 200° C.Thereafter, the aforementioned epoxy resin is cooled to roomtemperature.

In this step, the light emitting element LED and the light receivingelement PD are integrated with each other by the internal mold resinMRI. Specifically, the internal mold resin MRI is formed between thepotting resin PR and the light receiving element PD. Also, the internalmold resin MRI is formed to surround the potting resin PR, the lightreceiving element PD, and the region between them. The potting resin PRand the internal mold resin MRI are arranged between the light emittingelement LED and the light receiving element PD, but these resins have alight transmission property, as described above, and hence there is noobstacle to the transmission of an optical signal. For example, thetransmittance per mm of the thickness of each of the potting resin PRand the internal mold resin MRI is 10% or more for the light having awavelength within a range of 700 nm to 1000 nm. Further, the reflectanceper mm of the thickness thereof is 90% or less for the light having awavelength within a range of 700 nm to 1000 nm.

A withstand voltage can be improved by adopting such a double moldstructure (sealing body structure by the potting resin PR and theinternal mold resin MRI). The withstand voltage of the optical couplingdevice according to the present embodiment, the device adopting thedouble mold structure, is, for example, 10 kV or more.

Further, an epoxy resin composition, in which the ratio of an aromaticring is small, is used as described above, and hence deterioration ofthe resin can be suppressed. Even when the device is used particularlyunder a hot environment, as the case of an in-car optical couplingdevice, deterioration of the resin can be suppressed, and a decrease inthe light transmission property can be suppressed.

Thereby, the life of the device can be extended. Specifically, in a hightemperature-long term storage test, the properties can be maintained at150° C. for 10000 hours or longer, as described later.

Subsequently, the lead frames LF protruding from the internal mold resinMRI are sandwiched by the forming mold M2, as illustrated in FIG. 9. Inthis state, the epoxy resin composition is injected into the space(cavity) between the forming mold M2 and to the outer periphery of theinternal mold resin MR, and then subjected to a heat treatment. Thereby,the external mold resin MRO covering the internal mold resin MRI isformed. For example, a black epoxy resin cured product, or the like, canbe used as the external mold resin MRO. In the external mold resin MRO,the ratio of an aromatic ring may be larger than that of the internalmold resin MRI. A cured product of a composition in which, for example,the compound represented by the above formula (3) is used as a mainagent and the compound represented by the above formula (4) is used as acuring agent and a colorant, such as carbon, is added to them, can beused as the external mold resin MRO. For example, the aforementionedcomposition is injected into the space (cavity) between the forming moldM2, and then subjected to a heat treatment. Heating temperature is, forexample, approximately 160° C. to 200° C. Thereafter, the aforementionedepoxy resin cured product is cooled to room temperature.

Subsequently, the leads LD1 and LD2 are cut off from the lead frames LF,and the leads (outer lead parts) LD1 and LD2 each protruding from theexternal mold resin MRO are bent, as illustrated in FIG. 10. Herein, theleads LD1 and LD2 may be bent simultaneously with the cutting thereof.

The optical coupling device according to the present embodiment can beformed by the aforementioned steps.

As described above, an epoxy resin cured product, in which the ratio ofan aromatic ring is small, is used as the internal mold resin MRI in thepresent embodiment, and hence deterioration of the internal mold resinMRI can be suppressed.

FIG. 11 is a sectional view illustrating a configuration of an opticalcoupling device of First Comparative Example. In the optical couplingdevice in FIG. 11, for example, an epoxy resin composition, in which theratio of an aromatic ring is large, is used as the internal mold resinMRI.

Examples of the epoxy resin cured product in which the ratio of anaromatic ring is large include: a cured product using an epoxy resincontaining a benzene ring in a main agent (e.g., o-cresol novolac-basedepoxy resin, etc.); a cured product using a phenol-based curing agent asa curing agent; a cured product of the compound represented by theaforementioned formula (5); and the like. If such an epoxy resin curedproduct is used, a void is produced between the potting resin PR and theinternal mold resin MRI.

Occurrence of such a void will be described with reference to FIG. 12.FIGS. 12(A) to 12(C) are schematic views illustrating a mechanism bywhich a void is produced in a resin interface. There is no chemical bondin the surface of the potting resin (silicone resin cured product) PRcovering the light emitting element LED illustrated in FIG. 12(A), andhence the potting resin (silicone resin cured product) PR and theinternal mold resin (epoxy resin cured product) MRI are not chemicallybonded. Additionally, these resins are materials different from eachother, and hence the coefficients of thermal expansion thereof aredifferent from each other. For example, the coefficients of thermalexpansion of a silicone resin (400 ppm) and an epoxy resin (22 ppm) aredifferent from each other by one order or more. Accordingly, when theinternal mold resin (epoxy resin cured product) MRI is heated and thencooled to room temperature during the formation thereof, the interfacebetween the potting resin (silicone resin cured product) PR and theinternal mold resin (epoxy resin cured product) MRI is exfoliated asillustrated in FIG. 12(B), thereby causing a void S (FIG. 12(C)).

Further, if the void S is produced between the resins, the internal moldresin (epoxy resin cured product) MRI is discolored due to an influenceby the air (oxygen) in the void S. This discoloration will be describedwith reference to FIGS. 13(A) to 14. FIGS. 13(A) to 13(C) are schematicviews illustrating a mechanism by which the resin is discolored. FIG. 14is a view schematically illustrating a reaction in which an aromaticring undergoes oxidation discoloration. When the void S is produced inthe interface between the potting resin (silicone resin cured product)PR and the internal mold resin (epoxy resin cured product) MRI, asillustrated in 13(A), air (oxygen) enters the inside of the void (FIG.13(B)). The epoxy resin undergoes oxidation discoloration due to thisoxygen. In particular, an aromatic ring has high reactivity and a carboncompound radical (free radical) produced by oxidation combines with anaromatic ring (benzene ring), so that a C═C bond, C—C bond, C—R bond,and the like, are cut (FIG. 14). A benzene ring has a high electrondensity due to IC electrons, and hence it is likely to be attacked by afree radical. With this reaction, a new carbon compound radical (freeradical) is produced such that the reaction, in which the epoxy resincured product undergoes oxidation discoloration, progresses in a chainreaction (FIG. 13(C)). The oxidation discoloration reaction is likely toprogress particularly in a hot environment.

With such oxidation discoloration of the epoxy resin cured product, thelight transmission property of the epoxy resin cured product isdecreased, and the transmission performance for an optical signal isdegraded.

FIG. 15 is a sectional view illustrating a configuration of an opticalcoupling device of Second Comparative Example. As the optical couplingdevice of the Second Comparative Example illustrated in FIG. 15, whenthe potting resin (silicone resin cured product) PR is arranged, forexample, between the light emitting element LED and the light receivingelement PD, the interfaces between the potting resin (silicone resincured product) PR and the internal mold resin (epoxy resin curedproduct) MRI are produced on both the sides of the light emittingelement LED, and hence the epoxy resin cured product is littleinfluenced by an oxidation discoloration reaction. In other words,discoloration of the epoxy resin cured product, the discolorationintersecting the transmission path of an optical signal between thelight emitting element LED and the light receiving element PD, is nevergenerated. However, in the structure of the Second Comparative Examplein which the potting resin (silicone resin cured product) PR is arrangedbetween the light emitting element LED and the light receiving elementPD, a spark is generated between the light emission side and the lightreceiving side via the void S, thereby decreasing the withstand voltage.

On the other hand, by adopting a double molding structure (sealing bodystructure by the potting resin PR and the internal mold resin MRI), asin the present embodiment, the withstand voltage can be improved.Further, when an epoxy resin cured product, in which the ratio of anaromatic ring is small, is used, the progress of the aforementionedoxidation discoloration reaction can be suppressed. Thereby, degradationof the transmission performance for an optical signal can be suppressed.Furthermore, degradation of the transmission performance for an opticalsignal can be suppressed even under a hot environment, thereby allowingthe life at high temperature to be extended. For example, in a hightemperature-long term storage test, the properties can be maintained at150° C. for 10000 hours or longer.

FIGS. 16(A) to 16(C) are schematic views illustrating a mechanism bywhich discoloration of the resin is suppressed. Even if the void S isproduced as illustrated in FIG. 16 (A), the reaction, in which an epoxyresin cured product undergoes oxidation discoloration, is not likely toprogress by using the epoxy resin cured product in which the ratio of anaromatic ring is small, thereby allowing the oxidation discoloration ofthe epoxy resin cured product to be suppressed.

In order to make the ratio of an aromatic ring in an epoxy resin curedproduct small, an aromatic ring in a main agent is replaced by acycloaliphatic compound, as illustrated in FIG. 16(B). For example, abenzene ring is replaced by dicyclopentadiene. Additionally, in order tomake the ratio of an aromatic ring in an epoxy resin cured productsmall, a curing agent is changed from a compound having an aromatic ringto a compound excluding it, as illustrated in FIG. 16(C). For example,phenol is changed to an acid anhydride.

Example

The results of oxidation discoloration tests for epoxy resin curedproducts in which the ratio of an aromatic ring is small are shown inTable 1. Three types of an epoxy resin composition A, an epoxy resincomposition B, and an epoxy resin composition C were used as the epoxyresin compositions. Each of the epoxy resin compositions has a mainagent, in which the ratio of an aromatic ring is lowered, and a curingagent, in which the ratio thereof is lowered. An epoxy resin compositionin which the ratio of an aromatic ring is large, specifically, an epoxyresin composition, having a main agent containing o-cresol novolac and acuring agent containing phenol, was also tested in the same way, as acomparative example (Ref).

Each of the epoxy resin compositions was cured, and a sample thereof,having a thickness of 1 mm, was left in a thermostatic oven (in the air)at 150° C. for 500 hours. In this test, the surface of the epoxy resincured product is exposed to the air, and hence the test is a moreaccelerated test than a test performed in a manufactured product state.In a manufactured product state, the internal mold resin (epoxy resincured product) MRI is covered with the external mold resin MRO and thepaths through which air (oxygen) is supplied are few, and hence theprogress of discoloration is slower than the values shown in Table 1.For example, the degree of the discoloration of the epoxy resin curedproduct after 150° C. for 10000 hours in a manufactured product statecan be matched with the color of the epoxy resin cured product in thesample after 150° C. for 500 hours in the present test.

TABLE 1 initial state 24 H 48 H 168 H 300 H 500 H Rev. white light creamorange drown dark cream brown A white white white white white white Bwhite white white white white white C white white white white whitewhite

In the case of Comparative Example (Ref), the discoloration of thesample that was white in the initial state progresses with elapsed timeof 24 hours, 48 hours, 168 hours, 300 hours, and 500 hours, and thesample becomes dark brown after 500 hours, as illustrated in Table 1.

On the other hand, with respect to the epoxy resin compositions in whichthe ratio of an aromatic ring is lowered, the discoloration of thesample (epoxy resin cured product) using any of the compositions A to Cis not confirmed after 500 hours. It has been revealed that theproperties can be maintained at 150° C. for 10000 hours or longer in amanufactured product state by using an epoxy resin cured product inwhich the ratio of an aromatic ring is lowered.

CONCLUSION

Thus, by using, as a main agent (epoxy resin), a compound in which theratio of an aromatic ring is small, the ratio of an aromatic ring in theepoxy resin cured product becomes small, and hence deterioration of theresin can be suppressed.

An example of the epoxy resin in which the ratio of an aromatic ring issmall includes one containing an aromatic ring and an alicycliccompound. An epoxy resin cured product formed by curing the epoxy resincontains the aromatic ring and the alicyclic compound. The ratio of analicyclic compound in the epoxy resin or the cured product is preferably20% or more. The ratio of an alicyclic compound is calculated by (thenumber of alicyclic compounds/the total of the number of aromatic ringsand the number of alicyclic compounds in an epoxy resin or a curedproduct)×100%.

Alternatively, an epoxy resin or a cured product excluding an aromaticring may be used.

The aforementioned o-cresol novolac-type epoxy resin (main agent) isrepresented by the following formula (6):

In order to reduce the ratio of an aromatic ring, the compoundrepresented by the aforementioned formula (1) (dicyclopentadiene-typeepoxy resin (main agent)) is used in place of the compound representedby the formula (6). That is, the portion of a benzene ring is replacedby dicyclopentadiene (see FIG. 16(B)).

In this case, the ratio of an aromatic ring to an alicyclic compound is1:1 in the repeating unit structure (structure in the parenthesis) inthe main agent. For example, when an aromatic ring is indicated by A andan alicyclic compound by B, the structure is represented by -(A-B)n-. Inthis case, the ratio of an alicyclic compound becomes approximately 50%.

Alternatively, an epoxy resin using a nitrogen-containing ring (e.g.,triazine ring) may be used in place of an aromatic ring. Also in thiscase, the ratio of an aromatic ring becomes small. An example of anepoxy resin in which the ratio of an aromatic ring is small includes onecontaining an aromatic ring and a nitrogen-containing ring. An epoxyresin cured product formed by curing the epoxy resin also contains thearomatic ring and the nitrogen-containing ring. The ratio of anitrogen-containing ring in the epoxy resin or the cured product ispreferably 20% or more. Alternatively, an epoxy resin or a cured productexcluding an aromatic ring may be used.

Also, a compound excluding an aromatic ring (e.g., acid anhydride), orthe like, is used as the curing agent.

An epoxy resin cured product is used as the internal mold resin MRI inthe present embodiment, but a silicone resin cured product may be usedas that. A silicone resin cured product excludes a reflecting agent,such as titanium oxide, and has a light transmission property for thelight having the wavelength of an optical signal. For example, thetransmittance per mm of the thickness of the silicone resin curedproduct is 10% or more for the light having a wavelength within a rangeof 700 nm to 1000 nm. Further, the reflectance per mm of the thicknessof the silicone resin cured product is 90% or less for the light havinga wavelength within a range of 700 nm to 1000 nm. The binding energybetween atoms of a silicone resin cured product is larger than that ofan epoxy resin cured product, and hence a silicone resin cured productis less likely to be decomposed than an epoxy resin cured product.Further, if a silicone resin cured product is decomposed (oxidized), itbecomes a compound having a high light transmission property, such asSiO₂, and hence discoloration is not likely to be generated.Accordingly, degradation of the transmission performance for an opticalsignal can be reduced.

Second Embodiment

In the present embodiment, examples of the applications of the opticalcoupling device according to First Embodiment will be described.

A silicone resin cured product is used as the potting resin PR in FirstEmbodiment; however, of silicone resin cured products, a rubber-likesilicone resin cured product having a Shore A hardness of 15 to 30 maybe used as the potting resin PR.

By using such a silicone resin cured product, the transmission propertyfor an optical signal can be further stabilized, in addition to theadvantages of First Embodiment (improvement in a withstand voltage,extended life at high temperature).

It can also be considered that, for example, a gel-like, soft siliconeresin cured product having a low hardness (a Shore A hardness of lessthan 20) is used. By using such a gel-like, soft silicone resin curedproduct having a low hardness, the potting resin (silicone resin curedproduct) PR can be deformed to follow the concavities and convexities ofthe surface of the internal mold resin (epoxy resin cured product) MRI.In such a case, a void between the resins, which has been described inFirst Embodiment, can be filled (resins can be closely adheredtogether), and hence entry of oxygen can be reduced, and discolorationof the internal mold resin (epoxy resin cured product) MRI can bereduced.

However, a gel-like, soft silicone resin cured product having a lowhardness has a tackiness, and hence the position of the joint surfacebetween resins is likely to change due to a change in temperature(vertical change in temperature, reflow, temperature cycle, etc.). Forexample, when a temperature is changed (e.g., normal temperature (25°C.)→reflow temperature (260° C.)→cooling (25° C.)), the position andsize of the void S, located in the transmission path of an opticalsignal, are changed as illustrated in FIGS. 17(A) to 17(C). In thiscase, the transmission property for an optical signal is changed. Acohesive failure may also be caused. FIGS. 17(A) to 17(C) are schematicviews illustrating the states of voids, when a silicone resin curedproduct having a low hardness is used.

On the other hand, when a rubber-like silicone resin cured producthaving a certain hardness, for example, a Shore A hardness of 15 to 30is used, the void S may be caused and an influence by oxygen may becaused, but changes in the position and size of the void S becomes lessthan when a silicone resin cured product having a low hardness is used,as illustrated in FIGS. 18(A) to 18(C). Herein, with respect to aninfluence by oxygen, the problem of discoloration of the resin can beavoided by lowering the ratio of an aromatic ring in the epoxy resincured product described in First Embodiment. FIGS. 18(A) to 18(C) areschematic views illustrating the states of a void, when the siliconeresin cured product according to the present embodiment is used.

Thus, with a combination of a rubber-like silicone resin cured producthaving, for example, a Shore A hardness of 15 to 30 and an epoxy resincured product in which the ratio of an aromatic ring is small, thetransmission property for an optical signal can be stabilized, inaddition to the advantages of First Embodiment.

Third Embodiment

In the present embodiment, application examples of the optical couplingdevice described in First Embodiment or Second Embodiment will bedescribed. The places, to which the optical coupling device described inFirst Embodiment or Second Embodiment can be applied, are not limited,and for example, the device can be used in the power conversion systemdescribed below.

FIG. 19 is an illustrative view (circuit block view) illustrating oneexample of a power conversion system (power conversion apparatus)according to the present embodiment.

The power conversion system illustrated in FIG. 19 has a load, such as amotor MOT, an inverter (amplifier circuit part) INV, a power supply BAT,a controller (control circuit) CTC, and photocouplers (optical couplingdevices, optical coupling parts) PC. Herein, a three-phase motor is usedas the motor MOT. A three-phase motor is configured to be driven by avoltage having three phases different from each other. The photocouplerPC is an optical coupling part to be inserted between an electricalcircuit that forms the inverter INV and an electrical circuit that formsthe controller CTC. The photocoupler PC has a function to electricallyinsulate the inverter INV and the controller CTC from each other and totransmit a signal from the controller CTC toward the inverter INV.

In the power conversion system in FIG. 19, the power supply BAT is to becoupled to the inverter INV such that a voltage (power) of the powersupply BAT is supplied to the inverter INV.

Alternatively, a voltage to be supplied to the inverter INV may beconverted, or the coupling state between the power supply BAT and theinverter INV may be switched by interposing a non-illustrated converteror relay between the power supply BAT and the inverter INV. The motorMOT is coupled to the inverter INV, so that a DC voltage (DC power)supplied from the power supply BAT to the inverter INV is converted intoan AC voltage (AC power) by the inverter INV so as to be supplied to themotor MOT. The motor MOT is driven by the AC voltage (AC power) suppliedfrom the inverter INV.

The controller CTC is also coupled to the inverter INV, so that theinverter INV is controlled by the controller CTC. That is, a DC voltage(DC power) is supplied from the power supply BAT to the inverter INV,which is converted into an AC voltage (AC power) by the inverter INVcontrolled by the controller CTC and then supplied to the motor MOT,thereby allowing the motor MOT to be driven. The controller CTC isformed, for example, by an ECU (Electronic Control Unit), and has abuilt-in controlling semiconductor chip, such as an MCU (MicroController Unit).

The inverter INV has six IGBTs (Insulated Gate Bipolar Transistors) 10,corresponding to three phase. That is, in each of the three phase, theIGBTs 10 are coupled between a power supply potential (VCC) suppliedfrom the power supply BAT to the inverter INV and an input potential ofthe motor MOT, and between the input potential of the motor MOT and aground potential (GND), respectively.

The motor MOT is to be driven (rotated) by controlling a current flowingthrough the IGBT 10 with the controller CTC. That is, the motor MOT canbe driven by controlling ON/OFF of the IGBT 10 with the controller CTC.

In this case, if the inverter INV, through which a relatively largecurrent for driving the motor MOT flows, and the controller CTC, throughwhich a relatively small current, such as a control signal, flows, areelectrically coupled together, there is the concern that noise may becaused on the controller CTC side.

So, by inserting the photocoupler PC, having a function to electricallyinsulate the inverter INV and the controller CTC from each other and totransmit a signal from the controller CTC toward the inverter INV, asillustrated in FIG. 19, the reliability of the power conversion systemcan be improved.

Further, by using the optical coupling device described in FirstEmbodiment or Second Embodiment as the photocoupler PC to be used in theaforementioned power conversion system, the reliability of the powerconversion system to be improved.

The invention made by the present inventors has been specificallydescribed above based on preferred embodiments; however, it is needlessto say that the invention should not be limited to the preferredembodiments and various modifications may be made to the inventionwithin a range not departing from the gist of the invention. Forexample, a photocoupler is exemplarily described as an optical couplingdevice in First Embodiment; however, the resin described in FirstEmbodiment may be applied to an optical MOSFET.

What is claimed is:
 1. A manufacturing method of an optical couplingdevice, comprising the steps of: (a) providing both a first lead framehaving a first mounting part and a first lead and a second lead framehaving a second mounting part and a second lead; (b) mounting a firstelement over the first mounting part; (c) forming a first resin over thefirst element; (d) mounting a second element over the second mountingpart; and (e) facing the first resin over the first element and thesecond element with each other so as to form a second resin between thesecond element and the first resin, wherein the second resin is a curedproduct of a composition having an epoxy resin and a curing agent, andhas a light transmission property, wherein the epoxy resin contains anaromatic ring and an alicyclic compound, wherein the cured product ofthe second resin includes silica in a ratio of 60 to 90 wt % based onthe weight of the epoxy resin composition, and wherein the cured productis a compound represented by the formula:


2. The manufacturing method of an optical coupling device according toclaim 1, wherein the (e) step is a step of forming the second resin bythermally curing the epoxy resin with the curing agent.
 3. Themanufacturing method of an optical coupling device according to claim 1,wherein the epoxy resin excludes an aromatic ring.
 4. The manufacturingmethod of an optical coupling device according to claim 1, wherein theepoxy resin is an epoxy resin represented by the formula (1):


5. The manufacturing method of an optical coupling device according toclaim 4, wherein the curing agent excludes an aromatic ring.
 6. Themanufacturing method of an optical coupling device according to claim 1,wherein the first resin is a silicone resin cured product.
 7. Themanufacturing method of an optical coupling device according to claim 1,wherein a transmittance per mm of a thickness of the second resin is 10%or more for light having a wavelength within a range of 700 nm to 1000nm.
 8. The manufacturing method of an optical coupling device accordingto claim 1, wherein a reflectance per mm of the thickness of the secondresin is 90% or less for light having a wavelength within a range of 700nm to 1000 nm.